1. Field of the Invention
The present invention relates to a symbol information reading apparatus for reading symbol information such as bar codes.
2. Description of the Related Art
With the remarkable spread of POS (Point Of Sale) systems in recent years, bar codes have become familiar to the public. A bar code is a symbol consisting of bars and spaces combined in parallel to form a single bar code character. If necessary, character groups including check digits are added in parallel to the bar code character; for example, unique patterns of start and stop characters are appended before and after the bar code character to indicate the beginning and ending of a bar code symbol.
JAN (Japan Article Number) is a standardized bar code system widely used in Japan for general consumer goods. Another application of bar codes is as distribution material symbols which are such that a distribution identification code of one or two digits is placed before the JAN code to form one symbol.
Any bar code symbol of the above bar code systems is called a one-dimensional bar code. The amount of information that those bar code systems can handle is several tens of bytes at most.
Recently, however, there has been a strong demand for a bar code containing a greater amount of information. To meet the demand, various symbol systems called two-dimensional bar codes have been proposed.
With these symbol systems, a remarkably large amount of information can be coded as compared to the one-dimensional bar code systems. In one of two-dimensional systems, the amount of information is increased by stacking one-dimensional bar codes. The symbols of these system are called stacked bar codes. This type of stacked bar codes system includes a system called PDF-417.
A known symbol information reading apparatus for reading stacked bar codes is a laser scan type apparatus. According to this apparatus, a laser beam scans two-dimensionally, thereby reading and decoding the information contained in stacked bar codes.
Furthermore, Jpn. Pat. Appln, KOKAI Publication No. 2-268383 disclosed an apparatus wherein a bar code is taken by a two-dimensional imaging apparatus, the image data of the bar codes is stored in a memory, and the bar code symbol information is decoded on the basis of the image data stored in the memory.
However, the problem with these conventional bar-code symbol information reading apparatuses is that it is very time-consuming because the decoding process of bar-code symbol information obtained by scanning or imaging always takes place even when information necessary for decoding cannot be adequately obtained, or even when it is evident that decoding cannot provide the desired result. When decoding cannot be effectively performed, the bar code to be read must be scanned or imaged again to obtain the bar-code symbol information. In practice, however, the decoding process is always carried out, regardless of whether decoding is possible or not. Since this is not known immediately after the bar code has been scanned or imaged, time is wasted while waiting.